Vulcanization accelerator comprising a mixture of a heterocyclic mercaptan derivative and a thiocarbamyl aminomethyl sulfide



UNITED STATES PATENT OFFICE VULCANIZATION ACCELERATOR COMPRIS- ING AMIXTURE OF A HETE'RO'CYCLIC MERCAPTAN DERIVATIVE AND A 'THIO-" CARBAMYLAMINOMETHYL 'SULFIDE Roger A. Mathes, Akron, Ohio, assignor to The .B.F. Goodrich Company, New York, N. Y., a

corporation ofNew York No Drawing. Original application March 7, 1947,

'Serial No."7'33;191. Divided and this application June 26, 1950, SerialNo. 170,467

- 7 Claims. 1

This invention relates to "the "vulcanization of rubbery materials, andmore specifically pertains to the acceleration of the sulfurvulcanization of sulfur vu-lcanizable rubbery materials by use of anaccelerator combination consisting of a Waterinsoluble metal salt of aheterocyclic nitrogen- -con'ta'ining mercaptan and a th-ioca-rbamylaminomethyl sulfide.

'This application is a division-of my copend-ing application Serial No.733,191 filed March 7, 1 947,=-and'now abandoned.

Heretof'ore many disadvantages have been encountered in the industrialuse of thiocarbamyl aminomethyl sulfides asaccelerators for thevulcanization of sulfur-vulcanizable rubber materials. One of thesedisadvantages lies in the fact that the thiocarbamyl aminomethylsulfides volatilizeand/or decompose at the temperatures at which thecompounding and processing of rub- Ebery materials are ordinarilyefiected on a tactoryscale. In general, suchtemperatures are over 120 F.and usually within the range of 130 to 200 F.

Another undesirable property of the thiocarbamyl aminome'thyl sulfides,as far as industrial use is concerned, is that these compounds have atendency to cause premature vulcanization or scorching" in the rubbercomposition during compounding and processing, especially when asufiicient amount of the material is incorporated into 'the vulcanizablecomposition to compensate for that which decomposes and/or volatilizes,"or when the temperature of mixing is kept sufficiently low to preventthe dissipation of the thicc'arbamyl aminomethyl sulfide.

This premature vulcanization is highly undesirable since it producesisolated vulcanized masses "within the unvulcanized composition whichinterfere with further processing. For example, when a prematurelyvulcanized or 2 been directed to the prevention of their decompositionand/or volatilization and have not appreciably lessened their tendencyto cause ,pjrermature vulcanization.

vulcanization accelerators which are Waterinsoluble metal salts, such asthe lead and zinc salts, of heterocyclic nitrogen-containing mercaptans,also have a tendency to cause premature vulcanization of rubbercompositions in which they are incorporated, and this property isinvariably increased when the composition also contains a material whichactivates their-accelerating activity. r

I have "now discovered that :the disadvantages attending the use ofthiocar-bamyl aminomethyl sulfides as vulcanization accelerators areovercome by vulcanizing sulfur-vulcaniza'ble rubbery materials in thepresence, as the accelerator, of a mixture consisting of (1) awater-insoluble metal salt of a heterocyclic nitrogen-containingmercaptan and (2) a thiocarbamyl aminomethyl sulfide. When so proceedingthere is no volatilization or decomposition of the thiocarbamylaminomethyl sulfide during compounding and processing prior tovulcanization. Moreover, this mixture of vulcanization acceleratorsexhibits little or no tendency to 'cause premature vulcanization or'scorching in rubbery compositions. latter property is quite unexpectedsince, in general, the thiocar bamyl aminomethyl "sulfides function inrubbery compositions as activators for heterocyclic nitrogen-containingmercaptan accelerators and would be expected to increase the-soorc'h-ing tendency of the mercaptan salt rather than bringing about areduction of the scorching property.

Any desired thiocarbamylaminomethyl sulfides may be used in preparingthe accelerator mixtures used in this invention. Such compounds 40possess the following-general structural'iormula'z scorched compositionis processed to be used R, Tor molded goods, the composition willinotflow properly .to produce an acceptable molded artiole because "of theprematurely vulcanized ,particles. When such a composition iscalendered, Wh e fi a' hio y e upamine-st ucthe prematurely vulcanizedmasses are squeezed out by the calender rolls and snap back immediatelyafter passing through the rolls to form a hole in the thin calenderedsheet and when such a composition is extruded a rough article instead ofthe desired smooth article is produced.

.Some corrective methods have been suggested fora more efficient use ofthe thiocarbamyl aminomethyl-sul-fides as accelerators of vulcanizationbut most-of the corrective methods proposed have ture .drogen atom froma primary or secondary amine.

For example, R1-\ may be theunsubsti-tuted thioca-rbamyl .radical. ,orsubstituted .thiocaIi-bamyl radicals such as ldimethylthiocarbamy lidiethylthiocarbamyl, ethylbenzylthiocarbamyl, dibenzylthiocarbamyl,dicyclohexylthiocarbamyl, methyl phenylthiocarbamyl,diphenylthiocarbamyl phenyl-beta-naphthylthiocarbamyl,di-betanaphthylthiocarbamyl, di-xenylthiocarbamyl, di

-, m-, or p-tolyl-thiocarbamyl, dianthrylthiocarbamyl,cyclopentamethylenethiocarbarnyl derived from piperidine, cyclo(ethyleneoxy-ethylene)-thiocarbamyl derived .from morpholine, phenylthiocarbamyland other thiocarbamyl radicals of the structure. 7

wherein represents the residue derived by removing a hydrogen atom froma primary or secondary amine.

Similarly either or both of R2 and R3 in the amino methyl part of themolecule may be methyl, ethy1,iso propyl, cyclohexyl, benzyl,methoxymethyl, hy-

droxyethyl, aminoethyl or other alkyl, cycloalkyl, aralkyl,hydroxyalkyl, alkoxyalkyl or other aliphatic or alicyclic radicals, orsuch aromatic radicals as phenyl, tolyl, naphthyl, cumyl, cymyl,anthryl, phenanthryl, xenyl, anisyl, anilinophenyl, etc. Either R2 or R3may be hydrogen but not bothat the same time. R2 and R3 may be identicalgroups or they may be difi'erent- R2 and R3 may also be joined to formsuch cyclic groups as 'cyclopentamethylene derived from piperidine' andcycle (ethylene-oxy-ethylene) ,de-

rived from morpholine.

- Specific compounds within this class hereinbefore defined includedimethylthiocarbamyl dimethylaminomethyl sulfide, dimethylthiocarbamyldiethylaminomethyl sulfide, diethylthiocar- .bamyl diethylaminomethylsulfide, diethylthiocarbamyl dimethylaminomethyl sulfide,diethylthiocarbamyl cyclopentamethyleneaminomethyl sulfide,.cyclopentamethylenethiocarbamyl cyclopentamethyleneaminomethyl sulfide,cyclopentamethylenethiocarbamyl diethylaminomethyl sulfide,fdip'henylthiocarbamyl diethylaminomethyl sulfide, dimethylthiocarbamyldiphenylamino methyl sulfide, dimethylthiocarbainyl o, morp-tolylaminomethyl sulfide, cyclopentamethylenethiocarbamyldiphenylaminomethyl sulfide,

.cyclopentamethylenethiocarbamyl o, mor ptolylaminomethyl sulfide,diphenylthiocarbamyl anilinomethyl sulfide, cyclo(ethylene-oxy-ethylene)thiocarbamyl cyclo (ethylene oxy ethylene) -aminomethyl' sulfide,cyclo(ethyleneoxyethylene) -thiocarbamy1 diethylaminomethyl sulfide,cycl0(ethylene oxy ethylene) -thiocarbamyl anilinomethyl sulfide,cyclo(ethylene-oxyethylene) -thiocarbamyl o-, mor p-tolylaminomethylsulfide, phenyl-beta-naphthylthiocarbamyl cyclohexylaminomethyl sulfide,di-betanaphthylthiocarbamyl dimethyl aminomethyl sulfide and the like.

In general these thiocarbamyl aminomethyl tallic dithiocarbamate and anamine hydrochlo- R,-s-cH@-N NaCl H2O Ra where R1 'is the thiocarbamylgroup derived from the dithiocarbamate employed and R2 and R3 have thesame meaning as above. This reaction is readily carried out at atemperature of about 0 to 40 C.

The water-insoluble metal salt of a heterocyclic nitrogen-containingmercaptan which is combined with the thiocarbamyl aminomethyl sulfide'toform the mixture used according to this invention can be anyalkalineearth or heavy metal salt, such as those of calcium, barium, iron, zinc,lead, manganese, cobalt, and nickel, such heterocyclicnitrogen-containing mercaptans as mercaptoalkylthiazoles,mercaptoarylenethiazoles, mercaptooxazoles, mercaptothiazolines,mercapto oxazolines, mercaptothiazines, mercaptothiodiazoles,mercaptoquinolines, and mercaptothioimidazoles. Although anywater-insoluble metal salt of the above-named mercapto compounds can beemployed, I have found that the use of the zinc or lead salts ofheterocyclic nitrogen-containing mercaptans in which the heterocyclicring possesses the structure where X represents hydrocarbon structure,and

the mercapto group is connected to the carbon between the nitrogenandsulfur has given the best results and for this reason are thepreferred metal salts'for the purposes of this invention.

Preferably, the accelerator compositions used according to thisinvention are prepared in three steps. First, the water-insolublemetallic salt of the heterocyclic nitrogen-containing mercaptan isprepared by adding theheterocyclic nitrogencontaining mercaptan to anaqueous solution of sodium hydroxide to form the water-soluble sodiummercaptide and then a water-soluble salt of the desired metal such aszinc chloride or lead nitrate is added to the sodium mercaptide solutionto form the zinc or lead salt as a precipitate. Second, the thiocarbamylaminomethyl sulfide is then separately prepared as described above.Third, the two previously prepared slurries are mixed with stirring, theresulting slurry is filtered and the filtering cake is dried at about 50C. at atmospheric pressure. The dried product is usually a fine powderymaterial which may be difficult to handle in the mixing and compoundingwith rubber but this can be overcome by .in-

EXAMPLE I (A) 35 parts of 2-mercapto-4=,5-dimethylthia zole weredissolved in an aqueous sodium hydroxide solution containing 10 parts ofsodium hydroxide'in 600 parts of water. An aqueous solution containing.43 parts of lead nitrate in1250 parts or water wereadded to the sodiummercaptide'solution with stirring. A heavy yellow precipitate formedwhich is the lead salt of the mercaptothiazole.

(B) 23 parts ofa 25% by weight aqueous: solu- 'tion of dimethylaminewere added to 80 parts of water together with 1.0-parts of a 50% byweight aqueous solution of vsodium hydroxide I While stirring theresulting aqueous solution and maintaining a-re'action temperature ofabout 20- C 925 parts of carbon disulphide were slowly added to thereactionmixtura The product ofthis reaction thusfar' which isan aqueoussolution containing sodium vdimethyl dithiocarbamate was thentreactedwith 10.5 parts of a 37% by .weightaqueous formaldehyde solution and 1aparts of 'orthmtoluidine hydrochloride dissolved in 60 quarts of water.During this reaction the: temperature wasz maintained at 'about 20 C. byexternal cooling The resulting product, dime-th ylthiocarbam'ylortho-tolyl-aminomethyl sulfide,

acids commonly used in rubber compounding terials if desired withoutinterfering with the vulcanization accelerating activity of the mixtureof accelerators.

The mixture containing the water-insoluble salt of a hetero-cyclicnitrogen-containing mercaptan and a thiocarbamyl aminomethyl sulfidecanbe used with equal success as vulcanization accelerator either as thepreferred coated form or as the uncoated form, but the preferred formhas the advantage. of being more easily incorporated and dispersed inthe rubber composition. use of thesemi'xedaccelerators either in thecoated oruncoated form also provide an ad ditional advantage over eitherof the individual accelerator components in that there is no need tocool the'compoundingand processing equipment to prevent scorch'duringthe various steps encountered in factory processing procedures,

for, as itwill be demonstrated, these mixtures will not causeappreciable scorch even at 227 F. which is relatively high when comparedto the usual processing and compounding temperatures pheric pressure. 95parts of the dried products,

representing a 95% yield was recovered. This product was a practicallyodorless light brown powder which does not have a definite melting vpoint. The composition of this. resulting combination-productcorresponded to that of a prodnot containing 60% lead salt of the mercapto thiazole, 30%: of the thiocarbamyl aminomethyl sulfide and 10%. oil.

Other similar combination products were prepared in the same manner bysubstituting tor; the slurry of the leadsalt of 2-mercapto-4,5-dimethylthiazole slurries containing the same amounts by weight ofsuch-preferred metal salts' as the .zinc salt of2.-mercapto-4,5-dimethylp thiazole, th'e'zinc and lead salts of.z-mercaptoi 4,6,6-trimethylthiazine, 'the zinc and lead salts;

of 2.-mercaptobenzothiazole.and the zinc lead saltsofz-mercaptothiazoline. I

Such thiocarbamyl aminometh'yl sulfides, as forexample,,dimethylthiocarbamyl phenylaminomethyl sulfide,diethylthiocarbamyl diethylr-f aminomethyl sulfide, cyclopentamethylenethiocarbamyl cyclopentamethylene aminomethyl sulfide,diphenylthiocarbamyl diethylaminomethyl" sulfide," cyclo(ethyleneoxy-ethylenel-thiocaib-' amyl diethylaminomethyl sulfide and plienylbeta naphthyl --'thiocarbamyl cyclohex ylarninomethyl sulfide were alsoused with the above metal salts to prepare compositions of my invention.I

In preparing the accelerator.mixtures which are useful according to thisinvention, theratio of the metal salt to that of the thiocarbamylaminomethyl sulfide can be varied from "equal parts by weight of eachcompound to that of 5 parts of the metal salt tonne part of thethiocarbamyl aminomethyl sulfide, but the products containing thecomponents in a ratio of 2 parts of the metal salt to one part of thethiocarbamyl aminomethyl sulfide "has been found to give-the bestresults.

The process for preparing the mixed 7 accelerators in. theirpreferred-fenncan be varied in many: ways. For example, thecoatingmate'rial can be add'e'das' in Examp'le I, or may be added to thedry productresulting. from'the mixing of thetworshrrries and filtering.Also, 'oilsinfatty and of from 130 to 200 F.

A common method used to determine whether or not an accelerator ofvulcanization will cause prevulcanization or scorch is to incorporatethe accelerator in a sulfur vulcanizable composition and heat thecomposition at a. temperature which is relatively low as compared withthe temperatures usually employed tin vulcanizing' that particularrubber composition. If the tensile strength of the resulting heatedcomposition is low, the accelerator is said to be non-scorching.Accordingly, when the tensile strength of the resulting heatedcomposition is high the accelerator is said to be scorching.

In the following examples, the results of which are listed in tabular.formin Table I, the following tire tread stock compositions wereemployed, in which the parts by weight were prepared:

Composition A C'opol'ymer of butadiene -and styrene prepared in thepresence of rosin acid soap Channel Black; 47.5 Zinc oxide 2.5Antioxidant 1.0 Petroleum oil softener 10.0 Sulfur 2.0

Accelerator as noted in Table I Into the abovecomposition there wasincorporated the lead salt of 2-mercapto-4,5-dimethylthiazole,dimethylthiocarbamyl' ortho-tolylaminomethyl sulfide and the product ofExample I. The resulting mixtures were given the following designation.Example II, Composition A, plus 0.75 part of the lead salt of2-mercapto-4,5-dimethylthiazole. Example III, Composition A, plus 0.3part of dimethylthiocarbamyl orthotolylaminomethyl' sulfide. Example IV,Composition A,"plus 0.5 part of the product ofExample I.' Example V,Composition B, plus 1.5 part of the lead salt ofZ-mer'capto-j-dimethylthiaz'ole. Example VI, Composition B, plus 0.7part of dimethylthiocarbamyl ortho-tolylaminomethyl sulfide, and ExampleVII, Composition B, plus 0.8- part of the combination products ofExample I. The resulting mixtures were heated in a press at 227 F. forthe time shown in the following'table. The tensile strength of the testpieces was'determined and reported as T, the ultimate tensilestrehgthjin'pounds per square inch. The temperature of 227 F. isrelatively low for the vulcanization of tire tread composition andapproaches the temperatures incurred during compounding of such mixture.

TABLE I ar i 1 cam- Example zation in V T Min. at

60 V 950 so 1, on 60 375 120 350 120 1, 900 120 75 ,From acomparisonofthe tensilestrength of the vulcanizate of ExampleIV,prepared by the processor this" invention, with those my .thevulcanizatesor Examples IIra'nd III which employ the components utilizedto make the accelerator employed in Example IV, it is readily apparentthat theiproduct of Example I'is not as scorchy as is its components. Acomposition similar to that used in Example IV but containing 1.0 partof 2-mercapto benzothiazole, a commonly employed accelerator ofvulcanizationjwhen heated at 227? F, for 60 minutes has anultimatetensile strength of 70D lbs..'per sq. in. Accordingly, theproducts of Example I would be considered nonscorching. Froma,;simi1arcomparison of Example VII with Examples V and VI, it isapparent that the product of Example I is also non scorching in asynthetic rubber sulfur vulcanizable composition. I

The following Table II will further illustrate the results which can beobtained by following this invention. Example VIII is a compositionmade'up oi the ingredients of Composition A plus 0.5 part of the productof Exampl I, and Example IX is a. composition made up of'the ingredientsof Composition B plus 0.8 part of the product of Example I. Bothcompositions were vulcanized by'heatingat 280 F. in a. press for thetimeshown in Table II, where T is the ultimate tensile strength in poundsper squareinch and E is the percent elongation. Y

Without an accelerator, the rubber compositions A'and B should bevulcanized in about three a's-a polymer containing multiple isopreneunits) andsynthetic diene polymers. Examples of the latter include amongothers polymers of buta diene, isoprene, 2,3-dimethyl butadiene,piperylens and the -like, and "jcopolymers of thesecompoundswith-acrylonitril, styrene, methyl acrylate, methyl methacrylate,isobutylene and other 'copolymerizable monomers. fThese acceleratormixtures may be 'added' to the rubber on 'a roll mill. or in an internalmixer or by any other suitable method. 'Other compounding ingredientssuch as any 'of the ordinary pigments, fillers, antioxidants, or otheraccelerators of vulcanization may also be employed. Small quantities maybe used to achieve the desired result, either as vulcanizationactivators or accelerators. In general 0.1 to 5% or morebased on therubber composition may be used.

While'I have disclosed specific examples of my invention, I do notthereby desire or intend to limit myself solelythereto for as hithertostated the .precise proportions of the'materials utilized may be variedand other equivalent materials may be employed if desired-withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

.Iclaim:

1. The method of vulcanizing a sulfur-vulcanizable polymeric organicrubbery material which comprises incorporating into a mixture containingsulfurand said rubbery material from 0.1% to 5% by weight based on therubbery material of a composition comprising (1) a water-insoluble metalsalt of a heterocyclic nitrogen-containing mercaptan whose ringpossesses the structure wherein X- represents a hydrocarbon structureand in which the mercapto group is connected to the ring carbon atombetween the nitrogen and sulfur .atoms' and (2) a 'thiocarbamyl,aminomethyl sulfide of the'structure represents;a radical derived froman amine by removing a hydrogen atom attached to the, amine nitrogenatom, said composition containing 1 to 5 parts of the metal salt foreach part of the thiocarbamyl aminomethyl sulfide, and then heating theresulting mixture until vulcanized.

'2. The method of vulcanizing a sulfur-vulcanizable polymeric organicrubbery material which comprises incorporating intoa mixture contain- 9ing the rubbery material and sulfur from 0.1% to by weight based on therubbery material of a composition comprising (1) a lead salt of aheterocyclic nitrogen-containing mercaptan whose heterocyclic ringpossesses the structure N X c wherein X is a hydrocarbon structure andin which the merapto group is connected to the ring carbon atom betweenthe nitrogen and sulfur atoms and (2) a thiocarbamyl aminomethyl sulfideof the structur represents a radical derived from an amine by removing ahydrogen atom attached to the amine nitrogen atom, said compositioncontaining 1 to 5 parts of the lead salt for each part of thethiocarbamyl aminomethyl sulfide, and then heating the resulting mixtureuntil vulcanized.

3. The method of vulcanizing a polymeric organic rubbery material whichcomprises incorporating into a mixture containing the rubbery materialand sulfur from 0.1% to 5% by weight based on the rubbery material of acomposition comprising the lead salt of a 2-mercaptothiazole anddimethylthiocarbamyl ortho-tolyl-aminomethyl sulfide in the proportionof 1 to 5 parts of the lead salt for each part of the aminomethylsulfide, and then heating the resulting mixture until vulcanized.

4. The method of vulcanizing natural rubber which comprisesincorporating into a mixture containing natural rubber and sulfur from0.1% to 5% based on the rubber of a composition comprising the lead saltof 2-mercapto-4,5-dimethylthiazole and dimethylthiocarbamylortho-tolylaminomethyl sulfide in the proportion of 1 to 5 parts of thelead salt for each part of the aminomethyl sulfide, and then heating theresulting mixture until vulcanized.

5. The method of vulcanizing a rubbery copolymer of butadiene-1,3 andstyrene which comprises incorporating into a'mixture containing therubbery copolymer and sulfur from 0.1% to 5% by weight based on therubbery copolymer of a composition comprising the lead salt of2-mercapto-4,5 dimethylthiazole and dimethylthiocarbamylortho-tolyl-aminomethyl sulfide in the proportion 1 to 5 parts of thelead salt for each part of the aminomethyl sulfide, and then heating theresulting mixture until vulcanized.

6. A vulcanizate prepared by the method of claim 1.

7. A vulcanizate prepared by the method of' The following references areof record in the file of this patent:

UNITED STATES PATENTS Name Date Neal et a1 May 19, 1942 Number

1. THE METHOD OF VULCANIZING A SULFUR-VULCANIZABLE POLYMERIC ORGANICRUBBERY MATERIAL WHICH COMPRISES INCORPORATING INTO A MIXTURE CONTAININGSULFUR AND SAID RUBBERY MATERIAL FROM 0.1% TO 5% BY WEIGHT BASED ON THERUBBERY MATERIAL OF A COMPOSITION COMPRISING (1) A WATER-INSOLUBLE METALSALT OF A HETEROCYCLIC NITROGEN-CONTAINING MERCAPTAN WHOSE RINGPOSSESSES THE STRUCTURE